1. Field of the Invention
This invention relates to inhalers for bronchial or nasal administration of a dose of medicament in fine or micronized powder form.
2. Description of the Prior Art
Inhalers of this type are well known and can be divided substantially into two categories.
A first category comprises inhalers which use capsules normally formed of rigid gelatin or or another atoxic material. Each capsule contains a fixed quantity of powdered medicament forming the dose to be inhaled. Such inhalers comprise device for perforating or more generally opening (by various means) the capsule which is inserted into the inhaler when required.
An air stream generated by a sucking action by the user removes the contained powder from the opened capsule. The empty capsule is then expelled from the inhaler, which is then ready to receive the next capsule. In a known type of inhaler (see U.S. Pat. No. 3,906,950 and U.S. Pat. No. 4,013,075) the capsule when perforated at both its ends is held still during inhalation. The air stream which passes through it as a result of the inhalation removes the powdered medicament from its interior.
In another type of inhaler (see U.S. Pat. No. 3,807,400 and U.S. Pat. No. 3,991,761) the capsule, previously opened by suitable means, is set into movement by the action of the air stream produced by the inhalation, and is completely emptied thereby.
A further type of known inhaler (see EP-A-O 211 595) does not use individual capsules but instead is loaded with a disc-shaped pack comprising close to its periphery a series of blisters equidistant from each other and from the centre of the pack. These blisters contain a fixed quantity of powdered medicament. This pack is placed on a circular tray forming part of the inhaler and rotatable about its central axis. The tray contains holes in positions corresponding with the individual blisters and allows each blister to be moved into a predetermined position in which the blister is broken by a suitable opening device, so releasing the powder, which can then be inhaled.
Another type of inhaler, known as a multi-dose inhaler because it comprises a container containing a quantity of medicament sufficient for several doses, is described in EP-A-O 069 715 and in addition to the container comprises a device for withdrawing the powdered medicament contained in the container and for preparing the dose. This withdrawal and dose preparation device comprises a plate having a certain thickness and comprising a certain number of through holes. The plate can be moved from a position in which by mechanical means a proportion of the holes are filled with powdered medicament taken from the container, to another position in which the holes filled with medicament are located within a channel. Air flows into this channel as a result of suction provided by the user via a suction mouth in communication with the channel, to remove the powdered medicament from said holes. A scraper device is also provided to level the powder in the plate holes on that side facing the container. According to the inventor this scraper should ensure complete filling of said holes and consequently a constant dose. Although in the EP 715 document this scraper is stated to be optional, it must be considered essential for the proper operation of the inhaler because in its absence an extremely variable dose is obtained. This is because it is extremely easy for the respective holes not to be completely filled with powdered medicament because of the poor flowability of the powders used.
However even with the scraper present, the holes in the plate are not always completely filled, and there is thus an excessive dosage variability which, especially in the case of medicaments to be dispensed in very small doses, could result in substantial inactivity of the medicament.
Such multi-dose inhaler can also comprise rotary means (a rotatable impeller in the embodiment illustrated in EP-A-O 069 715) the purpose of which is to disintegrate any agglomerations of medicament particles.
Compared with inhalers using capsules containing a fixed quantity of medicament, multi-dose inhalers have undoubted advantages of convenience and marketability. However such inhalers suffer from substantial drawbacks particularly connected with the dose preparation device which, as already stated, is intrinsically unsuitable for dispensing sufficiently precise and constant amounts. The result is that powder quantities (doses) and hence medicament quantities are dispensed which do not conform to the declared quantity and are not constant. In addition the dispensed quantity is difficult to check by the appropriate authority.
Other drawbacks of known multi-dose inhalers are as follows:
although being single-piece devices, the powdered medicament contained in them is insufficiently protected, even if packaged in containers together with moisture absorption means; PA0 the powder drawn in is insufficiently mixed with the air (ie the resultant mixture contains an insufficient air quantity for the powder quantity drawn in at each inhalation); PA0 the air connections are always of small size, making them difficult to draw through by the user.